The present invention relates to a method for simultaneously producing styrene and benzene by reaction of toluene and ethylbenzene.
At the present time, styrene is made commercially by a multistep process starting with benzene which is alkylated with ethylene in the presence of a catalyst such as aluminum chloride to produce ethylbenzene which is then catalytically dehydrogenated to styrene. The dehydrogenation reaction is an endothermic one and its rate and the extent of conversion are limited by approach to thermodynamic equilibrium. The equilibrium limitation must be relieved in practice by low reaction pressures or by dilution with inert gases. It is well known that toluene can be dealkylated to benzene either thermally or catalytically by subjecting it in the presence of hydrogen to a temperature within the range from about 500.degree. to about 1000.degree.C at elevated pressure for a controlled period of time. As a result of such reaction conditions, the methyl group is cleaved from the toluene and replaced by hydrogen. The hydrodealkylation reaction is exothermic. It has now been discovered that these two reactions, the dehydrogenation of ethylbenzene and the hydrodealkylation of toluene, can be conducted either thermally or catalytically in the same reactor to provide a new method for producing styrene and benzene together utilizing less expensive reactants. The hydrogen and heat removal required in one reaction is provided by the other reaction taking place simultaneously. Energy requirements are reduced over the two separate processes, hydrodealkylation is effected at atmospheric or relatively low pressure, dehydrogenation is effected at atmospheric or higher pressure relative to those presently employed, no hydrogen recycle and clean-up is needed, hydrogen from the dehydrogenation of ethylbenzene reaction is effectively used without compression and capital costs are reduced as compared to requirements of two separte plants for separate production of styrene and benzene from ethylbenzene and toluene, respectively. It is especially remarkable that atmospheric pressure is successfully used in this dual reaction since the dealkylation of toluene alone requires at least 150 psi partial pressure of hydrogen to avoid aromatic condensation reactions leading to major yield losses to polynuclear aromatics. If desired, the ratio of benzene to styrene produced may be varied by modifications in process conditions.